Root Decomposition And Nutrient Dynamics Of Quercus Mongolica And Betula Platyphylla

Roots are important structural and functional components of forest ecosystems. Coarser roots in diameter play an important part in supporting and transporting. While the relatively finer roots are responsible for water and nutrients absorption. A large proportion of forest production is allocated to tree roots. Tree roots have higher turnover rates and root decomposition is the key link, resulting in a large flux of C and nutrients into the belowground system. Although tree root systems store large amounts of organic matter and nutrients in forest ecosystems, information on root decomposition is scant, especially compared with the wealth of data on aboveground litter decomposition. Also, past studies on root decomposition have primarily focused on fine roots while studies on coarser roots are almost none. Well then, how fast do the coarser roots decompose and how many C and nutients release due to coarser roots decomposition? To better and comprehensively understand the nutrient cycling, soil organic matter dynamics, and C stores of forest ecosystems, more sizes of root decomposition studies are needed. A buried bag experiment for the coarse (>10mm), middle coarse (5—10mm) and medium (2—5mm) of the two tree species and fine (<2mm) roots of the spring, summer and fall of the two tree species was conducted at Maoershan Forest Ecosystem Research Station. The root mass remaining rate showed a descending trend with time, which could be well fitted (with the R2>0.71) by the Olson negative exponential decay model (X/Xo=e-kt, where Xo is the initial dry weight, Xt is the dry weight remaining at the end of the investigation, t is the time interval and k is the annual decay constant). This study provided fundamental data for the C/N cycling in the natural generated forests in Northeast China. The results were as belows:1. The coarse, middle coarse, medium and fine roots of the oak had an annual decomposition coefficient of0.2928、0.2562、0.2928and0.3660, respectively, while the coefficients of those of the birch were0.2196、0.3294、0.3660and0.4392, correspondingly. After one-year decomposition,20%—33%of the mass was lost for roots with various diameters. The birch has higher concentrations of soluble sugars and N for the roots with same size, which was responsible for the higher decomposition rate for the birch. During root decomposition, N concentrations in all sizes of the roots increased, while the concentrations of soluble sugars exponentially decreased. N mass in the four root sizes of both species released or uptaken during different decomposition time with no consistent trend, but soluble sugar mass was always releasing during the study period. At the end of the study (one-year decomposition), all sizes of root of the oak, and the fine and medium roots of the birch were N source for the soil, but the coarse and middle coarse roots of the oak were N sink for the soil. More than90%of soluble sugars released from the fine and medium roots of the oak and birch, and more than80%of soluble sugars released from the coarse and middle coarse roots for the two species.2. Fine roots of the spring, summer and fall of the oak had an annual decomposition coefficient of0.3660、0.2178、0.2124, respectively, while the coefficients of those of the birch were0.4392、0.2541、0.2478. It showed that fine roots of the spring decomposed faster than roots of summer and fall for the two tree species. Fine roots of the three seasons of the birch decomposed faster than roots of the oak.